Camping well below freezing - Sweden over winter

I have camped in my Outfitter Apex at -20. The furnace never shut off and the inside temp never reached 50. The plumbing was dry, so no damage, but water and wastewater tanks will surely freeze without help. Folks who live in the far north where there is permafrost are 'up on stilts'. All wastewater drains into a tank below the house and gets hauled away. If I was spending any time camped at low temperature, I would open all the dump valves and get the waste outside.